The present invention relates to an electric corrosion preventing apparatus with a circuit having an indication lamp. This apparatus is used for preventing an inside wall of a hot-water receptacle, such as a water heater and a boiler, from being corroded by rust.
A conventional electric corrosion apparatus is shown in FIG. 1. As shown, a half-wave rectifying circuit having a diode 3 and a capacitor 4 is coupled with a secondary winding of a transformer 2 for dropping voltage of a commercial AC power source. A positive part of the output voltage is electrically connected to a corrosion prevention electrode 7 in water, supported by an insulating member mounted on a wall of a receptacle 5. A negative side of the output voltage is electrically connected to the receptacle 5. Reference numeral 8 represents a lamp and 9 is a resistor.
When the AC power source is turned on, a low AC voltage is developed in the secondary winding of the voltage-dropping transformer 2. A positive part a of the AC voltage developed as shown in FIG. 2 is rectified by half-wave and then smoothed to a DC current I as shown in FIG. 3. The current I is divided into a current I.sub.1 flowing through the resistor 9 into the lamp 8 and a current I.sub.2 flowing through a route of an electrode 7, the water 6 and the receptacle 5. The current I.sub.1 lights the lamp 8 to indicate that the power source is now turned on. The current I.sub.2 prevents the inner surface of the receptacle 5 from being corroded.
Resistance of the water 6 within the receptacle or a tank changes depending on the temperature and water quality. In the above construction, the current I.sub.2 accordingly changes depending on the above change. In accordance with the change of the current I.sub.2, the current I.sub.1 changes. When the current I.sub.1 is changed to low, the light intensity of the lamp is insufficient. On the other hand, when the current I.sub.1 is high, the life of the lamp 6 is undesirably shortened.
Because of the half-wave rectifying circuit for the power source circuit, the efficiency of the voltage-dropping transformer is undesirably poor, the transformer is bulky, and the capacitance of the capacitor 4 is large.